1. Technical Field
The present invention relates to an optical device and a method for manufacturing an optical device.
2. Related Art
As a polarizer used for an optical apparatus, a polarizer having a two-layer structure or three-layer structure is typically known in which a supporting layer made of triacetylcellulose (TAC) for securing mechanical strength and the like is stacked on one side or both sides of a polarizing layer made of polyvinylalcohol (PVA), for example, as disclosed in JP-A-7-20317. A supporting layer made of TAC has excellent transparency, uniformity, flatness and the like and has very little anisotropy due to molecular orientation. Therefore, it is preferably used as a supporting layer for supporting a polarizing layer.
Meanwhile, in a traditional polarizer, since light that is not transmitted through a polarizing layer is internally absorbed, a large quantity of heat may be generated, causing a rise in the temperature of the polarizer. Therefore, there is a problem that the polarizer is degraded, lowering the polarization characteristic of the polarizer.
Thus, as an optical device to solve such a problem, an optical device having a thermally conductive light-transmissive substrate bonded on both sides of a polarizer (outer side than the supporting layer of the polarizer) is disclosed, for example, in JP-A-2000-112022. With this optical device, heat generated in the polarizer is radiated outside of the system via the thermally conductive light-transmissive substrate, thus making it possible to restrain a rise in the temperature of the polarizer. Therefore, it is possible to restrain degradation of the polarizer and hence lowering of the polarization characteristic of the polarizer.
However, as the light sources in the recent optical apparatuses have increasingly higher luminance, a larger quantity of heat is generated in the polarizer and the temperature of the polarizer tends to rise easily. Therefore, the problem of degradation of the polarizer and lowering of the polarization characteristic of the polarizer due to the rise in the temperature of the polarizer tends to occur easily.